Portable directional device for locating neutron emitting sources

ABSTRACT

An apparatus for determining a direction of travel of a neutron emitted from a source includes: a chamber containing (i) nuclei that recoil upon interaction with an incoming neutron and (ii) atoms capable of being ionized by the recoiled nuclei thereby releasing electrons; an electron-interaction material disposed at the chamber and configured to receive electrons released by the ionized atoms and to emit photons upon the interaction with the received electrons; an imager configured to form an image of photons emitted by the electron-interaction material, wherein the image comprises a path having the direction of travel of the incoming neutron; and an orientation sensor configured to sense an orientation of the imager in order to relate the direction of travel of the incoming neutron to the orientation of the imager.

BACKGROUND

The present disclosure relates generally to detecting neutrons and, moreparticularly, to locating neutron emitting sources.

Special Nuclear Material (SNM) is defined as the type of material thatcan be used to fabricate a nuclear weapon. Detection of this type ofmaterial with a sensor is a challenge due to a variety of false alarms.Many of the false alarms can be due to natural sources common in manylocations and therefore difficult to avoid. Additionally, many of thefalse alarms are due to the phenomenology of the sensor design.

One way to detect SNM is to detect emitted gamma radiation, which comesfrom SNM sources. However, a large natural background of gamma radiationfrom cosmic sources and terrestrial sources, such as potassium-40 andIron-55, can cause false alarms. In addition, the SNM may be shielded togreatly reduce emission of associated gamma radiation and, thus, reducethe likelihood of detection.

Alternatively, SNM may be detected by detecting neutrons emitted fromthe SNM. Various processes such as nuclear absorption and excitationexist for neutron detectors to detect neutrons. In the nuclearabsorption process, a neutron is absorbed by the nucleus of some atom ina detector. This daughter nucleus will then decay emitting decayproducts such as charged particles or gamma radiation, which aresubsequently detected. While this process can detect thermal neutrons,it may not be efficient at detecting fast neutrons emitted from SNM.Additionally, it may be desirable to detect fast neutrons emitted bycontamination or radioactive leaks at nuclear power facilities orfacilities handling nuclear materials.

In the nuclear excitation process, an incoming neutron will scatter froma nucleus of some atom in the detector. This moves this nucleus to anexcited energy state from which it will return to a base state byemitting gamma radiation, which is then detected. These types ofdetectors have an inherent problem in that they are very good gamma raydetectors. They will detect noise such as typically all cosmicbackground radiation and all natural background gamma rays.

In addition to the above deficiencies, these types of neutron detectorstypically do not provide any directional information leading to a pointin space from where the detected neutrons came. Some types of neutrondetectors used for homeland security purposes do not lend themselves tomobility, but are generally permanently installed or difficult to move.Hence, improvements in neutron detection technology and, particularly,in portable neutron detectors would be well appreciated in the homelandsecurity industry as well as others.

SUMMARY

Disclosed is an apparatus for determining a direction of travel of aneutron emitted from a source. The apparatus includes: a chambercontaining (i) nuclei that recoil upon interaction with an incomingneutron and (ii) atoms capable of being ionized by the recoiled nucleithereby releasing electrons; an electron-interaction material disposedat the chamber and configured to receive electrons released by theionized atoms and to emit photons upon the interaction with the receivedelectrons; an imager configured to form an image of photons emitted bythe electron-interaction material, wherein the image comprises a pathhaving the direction of travel of the incoming neutron; and anorientation sensor configured to sense an orientation of the imager inorder to relate the direction of travel of the incoming neutron to theorientation of the imager.

Also disclosed is a method for determining a direction of travel of aneutron emitted from a source. The method includes: receiving anincoming neutron using a chamber that contains a nucleus that recoilsalong a direction of travel of the incoming neutron upon interactingwith the incoming neutron; ionizing atoms in the chamber to releaseelectrons along the direction of travel of the incoming neutron;emitting photons from an electron-interaction material upon interactingwith the released electrons along the direction of travel of theincoming neutron; creating an image of the emitted photons using animager, the image comprising a path having the direction of travel ofthe incoming neutron; and sensing an orientation of the imager using anorientation sensor coupled to the imager in order to relate thedirection of travel of the incoming neutron to the orientation of theimager.

Further disclosed is a non-transitory computer readable mediumcomprising computer executable instructions for determining a directionof travel of a neutron emitted from a source by implementing a methodthat includes: receiving an image created by an imager comprising a pathhaving the direction of travel of the neutron; receiving an orientationsensed by an orientation sensor attached to the imager in order torelate the direction of travel of the incoming neutron to theorientation of the imager; and determining the direction of travel ofthe neutron using the received image and the received orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1 is an exemplary embodiment of a portable neutron detection systemfor locating a neutron emitting source;

FIG. 2 is an exemplary illustration of an image of a path of a recoilednucleus having a direction substantially the same as an incomingneutron;

FIG. 3 is an exemplary illustration of a neutron-interaction materialfor emitting photons used to create an image of a path of the recoilednucleus;

FIG. 4 is an exemplary illustration of a tripod supporting a portableneutron detector that is included in the portable neutron detectionsystem; and

FIG. 5 is a flow diagram of an exemplary method for determining adirection from a neutron emitting source.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method is presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 illustrates an exemplary embodiment of a system 10 fordetermining a location of a neutron emitting source by determining adirection of a neutron from a neutron emitting source 2. The system 10includes a neutron detector 3 coupled to a processing system 4. Anorientation sensor 5 is also coupled to the neutron detector 3 and theprocessing system 4.

The neutron detector 3 is configured to detect an incoming neutron witha measurement of the detected neutron that is sensitive to the energyand direction of the detected neutron. The direction includes atwo-dimensional direction (e.g., direction in horizontal plane) or athree-dimensional direction (e.g. horizontal and vertical direction). Inorder to detect an incoming neutron, the neutron detector 3 includes achamber 6 containing a gas having various constituents. In one or moreembodiments, the gas contains a combination of CF₄ and Helium-4. When anincoming neutron enters the chamber, at some point it may undergo anelastic scattering interaction with a nucleus of one of the gaseousatoms. As a result of the interaction, the nucleus may recoil insubstantially the same direction as the direction of travel of theincoming neutron. In addition, the recoiled nucleus may gain energycorresponding to the energy of the incoming neutron. The recoilednucleus may then ionize atoms of the ionization gas contained in thechamber 6 to release electrons that interact with anelectron-interaction material 7. The ionization gas can be any gas suchas CF₄ that can be ionized by the recoiled nucleus. Upon interactingwith the released electrons, the electron interaction material 7 mayemit photons along the same direction as that of the received electrons.The emitted photons in turn are received by an imager 8, which forms animage of the received photons. The imager 8 includes a lens 9 configuredto focus the received photons onto an imaging plane 11. In one or moreembodiments the imager 8 is a charge-coupled device (CCD) camera. In oneor more embodiments, the image is formed by photon receptive pixels in asemiconductor sensor. It can be appreciated that the imager 8 can be anyelectronic camera, device or sensor that can record an image of thereceived photons and transmit that image to the processor 4. In theembodiment of FIG. 1, the electron interaction material 7 is in the formof a plate and the imaging plane 11 is parallel to the plane surface ofthe plate.

The electron-interaction material 7 may be any material that will emitphotons upon interacting with incoming electrons. In one or moreembodiments, the electron-interaction material 7 is a scintillator suchas any scintillator known in the art, preferably having a highcross-section for electrons. In one or more embodiments, theelectron-interaction material 7 is made of a metal and has a structuresuch that the metallic structure will emit photons (such as in the formof sparks) when the incoming electrons strike the metal. In onenon-limiting embodiment, the metallic structure may be a copper screenmesh. In one or more embodiments, the electron-interaction materialincludes an electron-amplifier region that may be created by a voltagegap in the electron-interaction material 7. The electron-amplifierregion is configured to initiate an avalanche of electrons from one ormore received electrons.

It can be appreciated that the atoms of the ionization gas are ionizedby the recoil nucleus along the direction of travel of the incomingneutron. Accordingly, the electrons released by the ionization arereleased also along the direction of travel of the incoming neutron. Theelectrons interacting with the electron-interaction material 7 alsointeract along the direction of travel of the incoming neutron and,thus, the emitted photons are emitted along the direction of travel ofthe incoming neutron. In turn, the imager 8 forms an image of theemitted photons that depicts the direction of the incoming neutron. Itcan be appreciated that the incoming neutron may enter the neutrondetector 3 at various angles. As long as the direction of the incomingneutron has a component that is parallel to a plane of theelectron-interaction material 7, the imager 8 may capture an image thatprovides that directional component in two dimensions. An exemplaryimage of a path of a recoiled nucleus is illustrated in FIG. 2. It canbe appreciated that the path or streak of light will be brighter at thestart of the track due to the recoiled nucleus having more energy toionize more atoms than at the end of the track. The length of the pathor streak may be related to the energy of the incoming neutron.Accordingly, the energy of the incoming neutron can be determined byanalyzing the intensity and/or length of the imaged path or streak oflight.

In one or more embodiments, the neutron detector 3 can determine thedirection of the incoming neutron in three dimensions. The thirddimension such as an angle α (i.e., vertical angle) from the horizontalplane (when image plane is horizontal) may be determined by at least oneof several techniques. In the first technique, the total number ofphotons emitted from the electron-interaction material 7 and received bythe imager 8 is counted using the imager 8 and the processor 4. Thetotal number of photons counted is related to the total energy of therecoiled nucleus, which is related to the energy of the incomingneutron. Thus, the total number of photons counted provides a measure ofthe total energy of the incoming neutron. The three-dimensional pathlength of the recoiled nucleus also provides a measure of the totalenergy of the recoiled nucleus and, thus, the energy of the incomingneutron. Hence, the total number of photons counted provides an expectedthree-dimensional path length of the recoiled nucleus. Next, a length ofthe two-dimensional path or streak of light imaged by the imager 8 maybe measured by, for example, counting pixels in an electronic imager andaccounting for the pixel pitch. The measured length of the imagedtwo-dimensional path is then compared to the expected three-dimensionalpath length of the recoiled nucleus. If the imaged path length is thesame as the expected path length, then the vertical angle is zero, suchthat the direction of the incoming neutron is parallel to the plane ofthe electron-interaction material 7 and the imaging plane 11. As thevertical angle increases, the length of the expected three-dimensionalpath of the recoiled nucleus will be greater than the two-dimensionalpath or streak of light imaged by the imager 8. Hence, if the verticalangle is α, the expected path length is EL and the measured path lengthis ML, then α can be solved for in the equation, cosine(α)=ML/EL.

In lieu of or in combination with the geometric analysis, the neutrondetector 3 can be calibrated in a laboratory using incoming neutrons ofknown energies entering at various vertical angles and recording imagerresponses for the various angles. In embodiments where the types ofSpecial Nuclear Materials (SNM) of interest are known such as, forexample, Pu-239, U-233, U-235, and etc., the neutron detector 3 may bespecifically calibrated for energies of neutrons emitted by thesematerials.

In another technique for determining the vertical angle, theelectron-interaction material 7 may be made of a plurality of layers 30of an electron-interaction material as illustrated in FIG. 3. In theembodiment of FIG. 3, each layer 30 is made of a copper screen mesh.Coupled to each layer in the plurality of layers is a voltage sensor 31,which provides a voltage measurement to the processor 4. Each voltagesensor 31 is configured to measure the voltage of the associated copperscreen mesh layer 30. The electrons released by ionization will interactwith one or more of the layers 30 and be sensed by the correspondingvoltage sensor 31 and counted by the processing system 4. A voltagesource 32 may be coupled to two layers 30 to create a voltage gap thatmay cause an electron avalanche upon interaction with one or morereceived electrons. The electron avalanche may cause electronamplification of the received electrons in order to amplify the emittedphotons to produce an enhanced image. This technique is similar to thefirst technique in that the length of the path of light (ML) in theimage is measured and the three-dimensional path length (EL) isestimated based on a measurement of the total energy of the incomingneutron. However, in this technique, the total energy of the incomingneutron is measured by counting the number of received electrons usingthe voltage sensors 31 coupled to the processing system 4. The totalnumber of electrons received by the electron-interaction material 7 isproportional to the total number of ionized electrons and the totalnumber of ionized electrons is proportional to the recoil nucleusenergy. The recoil nucleus energy is in turn related to the energy ofthe incoming neutron. Thus, the collection of electrons in theelectron-interaction material 7 may be used to determine the angle α asin the first technique.

In lieu of or in combination with the geometric analysis, the neutrondetector 3 can be calibrated in a laboratory using incoming neutronsentering at various vertical angles and recording the correspondingvoltage measurements for the screen mesh layers for the various angles.In one or more embodiments, the number of layers 30 can range from fiveto fifty although more or fewer layers may also be used. It can beappreciated that as the number of layers 30 increases the accuracy andprecision of determining the vertical angle also increases.

In yet another technique, the electrons received by theelectron-interaction material 7 may be recorded as a function of time toproduce a series of received electron arrival times. The angle α may bedetermined by analyzing the arrival times of the individual receivedelectrons using the processing system 4. The electrons ionized by therecoil nucleus traveling parallel to a plane of the electron-interactionmaterial 7 will arrive at the electron-interaction material 7simultaneously, while electrons ionized by the recoil coil nucleustraveling with a vector component perpendicular to the plane will arrivewith arrival times spread out over a longer interval. The arrival timedistribution of the received electrons may be used to determine theangle α.

In lieu of or in combination with the geometric analysis, the neutrondetector 3 can be calibrated in a laboratory using incoming neutronsentering at various vertical angles and recording the correspondingelectron arrival time distributions for the various angles.

Referring again to FIG. 1, the processing system 4 is configured toreceive an image from the imager 8 and an orientation of the neutrondetector 3 from the orientation sensor 5. The orientation sensor 5, inone or more embodiments, may be an electronic digital compass, whichindicates direction by sensing the earth's magnetic field and transmitsthe sensed direction to the processing system 4. In one or moreembodiments, the orientation sensor 5 may be a Global Positioning System(GPS) device configured to determine a direction with respect to truenorth. In one or more embodiments, the sensed or determined direction istransmitted via a USB (Universal Serial Bus) connection. In one or moreembodiments, the electron-interaction material 7 or the imager 8includes a reference line such that the orientation sensor 5 candetermine the orientation or direction of the line in two-dimensionalspace. From this information, the processor 4 can be configured todetermine the direction of the imaged path with respect to the referenceline (angle β in FIG. 1) and, thus, with respect to magnetic or truenorth.

The system 10 for locating a direction from a neutron emitting sourcecan assume various configurations. In one or more embodiments, theneutron detector 3, the orientation sensor 5, and the processor 4 aremechanically coupled together to form a single unit. Alternatively, theprocessor 4 can be disposed remote from the neutron detector 3 and theorientation sensor 5, which are mechanically coupled together. In thisembodiment, an interface 12 (wireless, wired, or optical) may transmitthe image from the imager 8 and the measured orientation from theorientation sensor 5 to the processor 4 for processing. In yet anotherembodiment, the neutron detector 3, the orientation sensor 5, and theprocessor 4 are mechanically coupled together to form a single unit andthe interface 12 transmits a computed direction of the neutron emittingsource to a remote receiver. It can be appreciated that the utility ofthe system 10 can be increased by mechanically coupling a tripod 40 tothe neutron detector 3 as illustrated in FIG. 4. Because the system 10may be portable, the tripod 40, generally a folding tripod, can decreasethe deployment time of the system 10.

FIG. 5 is a flow diagram illustrating a method 50 for determining adirection of travel of a neutron emitted from a source in accordancewith an exemplary embodiment. The direction is generally the directionfrom the neutron emitting source to the neutron detector 3 and isgenerally determined with respect to magnetic or true north. However,other directional measurement systems or units may be used. Block 51calls for receiving an incoming neutron using a chamber that contains anucleus that recoils along a direction of the incoming neutron uponinteracting with the incoming neutron. Block 52 calls for ionizing atomsin the chamber to release electrons along the direction of the incomingneutron. Block 53 calls for emitting photons from anelectron-interaction material upon interacting with the releasedelectrons along the direction of the incoming neutron. Block 54 callsfor creating an image of the emitted photons using an imager, the imagecomprising a path having the direction of the incoming neutron. Block 55calls for sensing an orientation of the imager using an orientationsensor coupled to the imager in order to relate the direction of travelof the incoming neutron to the orientation of the imager. Conversely,the direction to the neutron emitting source from the neutron detectorcan be determined by adding 180 degrees to the determined direction fromthe source.

It can be appreciated that the system 10 has several advantages. Onadvantage is that the system 10 is portable. In one embodiment, theneutron detector 3 may have a cylindrical shape with a diameter ofthree-quarters of a meter and a length of one meter. However, it canalso be made larger or smaller. Hence, the system 10 can be quicklytransported, such as by motor vehicle, train, or aircraft, with littleeffort to a location perceived as posing a threat. Another advantage isthe ability to quickly deploy or setup the system 10 upon arrival at theselected location. The orientation sensor 5 coupled to the imager 8precludes the need of a survey team to survey the location for placementof the system 10.

In support of the teachings herein, various analysis components may beused, including a digital and/or an analog system. For example, theprocessing system 4, the orientation sensor 5, the imager 8, or thevoltage sensor 31 may include the digital and/or analog system. Thesystem may have components such as a processor, storage media, memory,input, output, communications link (wired, wireless, optical or other),user interfaces, software programs, signal processors (digital oranalog) and other such components (such as resistors, capacitors,inductors and others) to provide for operation and analyses of theapparatus and methods disclosed herein in any of several mannerswell-appreciated in the art. It is considered that these teachings maybe, but need not be, implemented in conjunction with a set of computerexecutable instructions stored on a non-transitory computer readablemedium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic(disks, hard drives), or any other type that when executed causes acomputer to implement the method of the present invention. Theseinstructions may provide for equipment operation, control, datacollection and analysis and other functions deemed relevant by a systemdesigner, owner, user or other such personnel, in addition to thefunctions described in this disclosure.

Elements of the embodiments have been introduced with either thearticles “a” or “an.” The articles are intended to mean that there areone or more of the elements. The terms “including” and “having” areintended to be inclusive such that there may be additional elementsother than the elements listed. The conjunction “or” when used with alist of at least two terms is intended to mean any term or combinationof terms. The term “couple” relates to one component being coupledeither directly to another component or indirectly via one or moreintermediate components.

The flow diagram depicted herein is just an example. There may be manyvariations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the disclosure has been described with reference to a preferredembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the disclosure.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the disclosure withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the disclosure not be limited to the particular embodimentdisclosed as the best mode contemplated for carrying out thisdisclosure, but that the disclosure will include all embodiments fallingwithin the scope of the appended claims.

What is claimed is:
 1. An apparatus for determining a direction oftravel of a neutron emitted from a source, the apparatus comprising: achamber containing (i) nuclei that recoil upon interaction with anincoming neutron and (ii) atoms capable of being ionized by the recoilednuclei thereby releasing electrons; an electron-interaction materialdisposed at the chamber and configured to receive electrons released bythe ionized atoms and to emit photons upon the interaction with thereceived electrons; an imager configured to form an image of photonsemitted by the electron-interaction material, wherein the imagecomprises a path having the direction of travel of the incoming neutron;and an orientation sensor configured to sense an orientation of theimager in order to relate the direction of travel of the incomingneutron to the orientation of the imager.
 2. The apparatus according toclaim 1, further comprising a processor configured to receive the imageand the orientation of the imager and to determine the direction oftravel of the neutron emitted from the source using the image and theorientation.
 3. The apparatus according to claim 1, wherein the electroninteraction material comprises a plane and the direction of travel isdefined in two dimensions within the plane.
 4. The apparatus accordingto claim 1, wherein the direction is defined in three dimensions.
 5. Theapparatus according to claim 4, wherein the processor is furtherconfigured to: count a total number of photons emitted by theelectron-interaction material; determine an expected three-dimensionalpath length (EL) of a nucleus recoiled by an interaction with theincoming neutron using the counted total number of photons; measure alength of the path (ML) in the image; and determine an angle (α) of thedirection of travel of the incoming neutron with respect to the plane inthe electron-interaction material using the length of the path in theimage and the expected three dimensional path length.
 6. The apparatusaccording to claim 4, wherein the electron interaction materialcomprises a plurality of layers in a configuration where one or more ofthe layers interact with the received electrons
 7. The apparatusaccording to claim 6, wherein each of the layers comprises a copperscreen mesh.
 8. The apparatus according to claim 7, the apparatusfurther comprising a voltage sensor coupled to each of the layers and tothe processor, wherein the processor is configured to: count the totalnumber of electrons received in the electron-interaction material;determine an expected three-dimensional path length (EL) of a nucleusrecoiled by an interaction with the incoming neutron using the countedtotal number of electrons; measure a length of the path (ML) in theimage; and determine an angle (α) of the direction of travel of theincoming neutron with respect to the plane in the electron-interactionmaterial using the length of the path in the image and the expectedthree dimensional path length.
 9. The apparatus according to claim 7,further comprising at least one voltage source coupled to at least twoof the layers and configured to apply a voltage difference to the layersto create an avalanche of electrons from one or more received electronsin order to amplify a number of photons emitted by the electroninteraction material.
 10. The apparatus according to claim 1, whereinthe image further comprises information related to an energy of theincoming neutron.
 11. The apparatus according to claim 1, wherein theimager comprises an imaging plane and the electron-interaction materialcomprises a plane that is parallel to the imaging plane.
 12. Theapparatus according to claim 1, further comprising a lens configured tofocus the released electrons onto the imager.
 13. The apparatusaccording to claim 1, wherein the orientation sensor is configured tosense an earth's magnetic field to determine the orientation of theimager or to use Global Positioning System information to determine theorientation.
 14. The apparatus according to claim 1, wherein theprocessor is further configured to determine an angle β of the path inthe image with respect to a reference line.
 15. The apparatus accordingto claim 1, wherein the imager comprises a charge-coupled device camera.16. A method for determining a direction of travel of a neutron emittedfrom a source, the method comprising: receiving an incoming neutronusing a chamber that contains a nucleus that recoils along a directionof travel of the incoming neutron upon interacting with the incomingneutron; ionizing atoms in the chamber to release electrons along thedirection of travel of the incoming neutron; emitting photons from anelectron-interaction material upon interacting with the releasedelectrons along the direction of travel of the incoming neutron;creating an image of the emitted photons using an imager, the imagecomprising a path having the direction of travel of the incomingneutron; and sensing an orientation of the imager using an orientationsensor coupled to the imager in order to relate the direction of travelof the incoming neutron to the orientation of the imager.
 17. The methodaccording to claim 16, further comprising determining the direction oftravel of the neutron using a processor that receives the image and thesensed orientation.
 18. The method according to claim 17, furthercomprising determining an angle of the path in the image with respect toa reference line and an angle of the reference line with respect to theorientation sensed by the orientation sensor to determine a directionfrom the imager to the source in order to determine the direction fromthe source.
 19. The method according to claim 17, further comprisingtransmitting the image and the orientation to the processor using awireless interface.
 20. A non-transitory computer readable mediumcomprising computer executable instructions for determining a directionof travel of a neutron emitted from a source by implementing a methodcomprising: receiving an image created by an imager comprising a pathhaving the direction of travel of the neutron; receiving an orientationsensed by an orientation sensor attached to the imager in order torelate the direction of travel of the incoming neutron to theorientation of the imager; and determining the direction of travel ofthe neutron using the received image and the received orientation.